If GPT4 is 20x the price of GPT3.5, but it only takes 10x GPT3.5 runs to get similar quality of response (and likely faster), you'll still come out ahead.
I doubt that 10xGPT3.5 > GPT4. There are a lot of tasks that GPT4 can do and GPT3.5 just cannot. Also, in such cases I find that GPT3.5's hallucinations are quite consistent, so such a method is probably not gonna help.